Static RPM - Catto Prop - O320...

[Michael Burbidge]

Yesterday I started my engine for the first time. I have an Lycoming O320-D3G (160 HP) carbureted engine. My A&P timed the mags on friday, so I know they are set correctly.

I have a new (shipped to me Feb 2013) 3 blade Catto Prop. Here's the specs on the prop:

3-Bladed Glass/Carbon Composite Propeller for RV-9A
68" Diameter x 70" Pitch
O320-D3G 160HP@2700RPM
Top Speed at Target RPM- 189-193mph@2750rpm
4.375" Finished Propeller Thickness
7" Diameter Prop Flange
SAE-2 Pattern, 7/16" Bolts and 5/8" Lugs
Color: WHITE W/ RV-14 Blue Crescent Tips

I have an analog tachometer, so I can't see exactly what the RPM is, but it is hovering just a hair under 2000 RPM. This seems low. I was expecting more like 2100 - 2200.

I've searched the forums and there's is lots of information on static RPM, but the solution always seems to be re-pitch the prop. But according to what I've read and the specs that Catto sent to me, it appears to be pitched about right.

What I'm looking for is the diagnostics steps that you would take and what order you would take them in to determine if the problem is something other than the prop.

Here are some things that I can think of, and the order I will probably take in diagnosing this problem. Also a question or two for each one.

1) Throttle travel is not adjusted correctly. How's the best way to determine if the throttle is full open when the throttle control is full forward. I have a manifold pressure gauge. Can that help in determining if I'm developing full power?

2) My tachometer is not accurate. How can you verify the tachometer reading?

3) My FAB scoop opening is smaller in area than the carburetor throat. Just a thought. I have no idea, if you build to plans how much head room there is here. My intention was to build to plans. I can test this theory by removing the FAB and checking the static RPM. I have not installed the alternate air yet, or it would be easy to just pull the alternate air.

Are there other things that could be wrong other than the prop?

Thanks for any help,
Michael-

[AX-O]

First thing i would do is check the tach. You can do it a few different ways. One of them is with dynamic balancing equipment. Another is using something like this http://www.proptach.com/specs.html

My static rpm on the ground was 2040 rpm on the first Catto i flight tested (new gen, 2 blades)

The new gen, 3 blade does 2100 rpm and turns 2710-2720 rpm at 11,500 ft.

[N941WR]

Adjust the throttle cable so it hits the stop on the carb with just a little cable movement left.

When you pull it to idle, the limit should be when the throttle arm hits the other stop.

[crabandy]

68X74 from March 2013 on an O-360 yields 2070 static and 2750 at 6000 density altitude.

[penguin]

Originally Posted by Michael Burbidge

I have an analog tachometer, so I can't see exactly what the RPM is, but it is hovering just a hair under 2000 RPM. This seems low. I was expecting more like 2100 - 2200.

Michael,

I have a 6A with a 160hp O-320 and have recently tested another type of wooden propeller. I would agree with your expectation for your prop - do you have access to a optical digital tacho that will sit on the coaming? If everything on the airplane is accurate I would send it back for a re-pitch.

2000rpm on the ground (what is your density alt?) will make your take-off performance sluggish compared to turning ~2150rpm. If you have a reasonably long runway (>3000' with good approaches) I would not delay flying, just be aware that the initial acceleration and climb performance may not be what you were expecting.

Pete

[Michael Burbidge]

I don't have an optical digital tach. But I can probably borrow one from someone around here or I will just take the airplane over to the FBO and have them check it.

I'm at Paine Field in Everett Washington. The elevation is 620 feet, and it was a mild day. So density altitude would be close to elevation.

Runway length is 9000 ft.

Thanks,
Michael-

[Michael Burbidge]

After adjusting the throttle travel and the idle mixture I'm now getting 2100. That's better. Looking forward to flying soon!